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How to fix: Serial Port 'COM3' not found.

New Member

My arduino is working on my pc until I tried to connect my other Arduino on my pc, and an error occured, and showed below: Serial Port 'COM3' not found. Did you select the right one from the Tools > Serial Port menu? Thus, the Serial Port on the Tools menu is not highlighted. Can someone who is expert or well-known in Arduino help me with this problem? Please I really need it as soon as possible, Thank you.

Well-Known Member

I can offer a couple suggestions but would also have to ask a few questions too.

First, does this happen with only one board or all your Arduino boards?
Also, are you trying to use a USB 3.0 port or a USB 2.0 port?
Another question, what kind of Ardu board are you using (Uno, etc.)?

I ask about the port type because some of the Arduino's do not work in some USB 3.0 ports but work fine in USB 2.0 ports.

I can offer a suggestion or two for now...

You can try unplugging the board then plugging it back in.
You can try closing down the IDE, then restarting it.

You can go into Device Manager and see if your Arduino is listed there, or at least the COM 3 port. This helps troubleshoot because you'll see the listing change when you plug in the board, if it is working properly. If it is not working properly, then you will see something different and that will tell you right away that you have to unplug it and plug it back in for example
If using a USB hub, that may need to be unplugged and plugged back in again too, and even might need to reboot the computer to get it to work properly. Sometimes hubs can work for some things but not other things until they are unplugged and plugged back in again.
Last resort, reboot the computer.

If nothing ever helps with a given board it could be a bad board too, or a fake USB to RS232 converter chip on board that Windows has recognized as fake and shut it down. This should not happen any more but i guess it is always a possibility. The only thiing i can think of here is to try the board in a computer with another operating system like maybe XP.

If you give more details about what you are using and what exactly you are experiencing, maybe someone here can help more. It might also help to know where you purchased the board from.

In the mean time, good luck with it.

One test is worth a thousand expert opinions, but one expert specification is worth a thousand tests.
Mathematics is the shortcut to understanding nature.
If i miss something you posted or something you think is important, feel free to PM me.

New Member

Actually what I have here is 3 Arduino, whereas; I have 2 clone Arduino, both are ATMEGA644, bought at the same store, but only 1 was working. And the other one is a genuine Arduino but not working. So it only happens in my 2 arduino.

Now, I do not know if it is USB 3.0 or USB 2.0 the port I am using. The ardu board I am using is MEGA2560,.

I already tried few of your suggestions, such unplugging ang plugging back the board, restarting the IDE, restarting my pc. But wheb I checked my device manager, the COM3 port does not appear. Do you think, it isbthe problem?

Well-Known Member

Actually what I have here is 3 Arduino, whereas; I have 2 clone Arduino, both are ATMEGA644, bought at the same store, but only 1 was working. And the other one is a genuine Arduino but not working. So it only happens in my 2 arduino.

Now, I do not know if it is USB 3.0 or USB 2.0 the port I am using. The ardu board I am using is MEGA2560,.

I already tried few of your suggestions, such unplugging ang plugging back the board, restarting the IDE, restarting my pc. But wheb I checked my device manager, the COM3 port does not appear. Do you think, it isbthe problem?

Well, from what you have said so far (one is working and the other two are not working) then it sounds like, on the surface of it, that two of the boards are defective.

There's one other possibility, and that is that the one 'good' board has a different USB controller chip than the other two (no matter where they came from) and those two controller chips dont work well with USB 3.0 and you are using USB 3.0 ports. That would mean the other two boards would work if plugged into a USB 2.0 port. It's hard to say for sure though, but obviously something is wrong and it's either the two boards or the two controller chips or the USB port. You could also try another USB port.
Note that most USB 3.0 ports have a blue colored plastic insert in the port jack, while USB 2.0 ports are usually red. The USB 3.0 ports may also appear to be 'upside down' as compared to the USB 2.0 ports. You could check those details.
There is also the possibility that the USB controller on the Arduino board needs reflashing, but you'd have to check the Arduino site for information on that, and even if your boards have a chip that can be reflashed (with the firmware).

All things considered so far, the best bet for you i would say is to try those three cards in another computer making sure to note which one works in your original computer and which two dont. You dont have to install the IDE, just look in Device Manager as suggested elsewhere. Look for an added port when you plug it in, or the name of the board in Device Manager.
This will tell you pretty much for sure if the boards are really bad or just dont work with your computer's port controller for some reason.
It might be best to test them one at a time too, so after you test one, unplug the board and plug the next one it.
Also, use a known good USB cable for all the tests.

Another thing i would ask is, do the two bad boards power up? Can you see LED's lit? Do they have the notorious 'Blink' program loaded in them (you'd see one LED blinking on and off)?

I wish you all the luck, and hope you get this resolved. You may have to send the boards back if it turns out that they are really bad. Can you mention where you purchased them? If you dont want to that's ok too, but thought it might be worthwhile knowing that too.

Last edited: Feb 26, 2016

One test is worth a thousand expert opinions, but one expert specification is worth a thousand tests.
Mathematics is the shortcut to understanding nature.
If i miss something you posted or something you think is important, feel free to PM me.